The invention pertains generally to data storage and in particular to holographic data-storage.
The increases in size and complexity of computers along with the increase in storage and data-processing requirements have created a need for fast, high-density write-read-erase memories with capacities exceeding 10.sup.9 bits and submicrosecond random-access times. By employing the three dimensionality and inherent parallel-processing capability of holography, a larger storage capacity is obtained without sacrificing access time. By contrast, conventional computers must be designed as a compromise where there is a trade-off between these two parameters.
Essentially holographic data storage is achieved by recording an interference pattern between a reference light wave and the object light wave scattered from a transparency on which data is recorded. Best results have only been obtained for off-axis arrangements of the reference and object waves, wherein a separation is achieved during holographic reconstruction of the virtual image which is usually the desired data plane from all other waves, i.e., the real image and the on-axis waves.
Unfortunately, holographic data storage is not without problems. These often include light scattering from the stored material, graininess of the storage medium, contamination of the data readout by noise introduced by interference with the on-axis transmissions of the hologram. The latter results in a trade-off between the readout size and the readout modulation of brightness.